Some touch sensors are configured to detect touch input by sensing changes in capacitance between row electrodes and column electrodes of an electrode matrix. Touch inputs may be from a user's body (e.g., a finger) and, in some cases, an active stylus. In active-stylus implementations, the stylus may be synchronized with the touch sensor in order to achieve a shared sense of time between the stylus and touch sensor. This may, among other things, facilitate determinations of stylus position relative to the touch sensor.
Multiple rows of the matrix may be driven simultaneously with a synchronization waveform. Via capacitive coupling, this causes current to flow into a tip electrode of the stylus. The current pattern is processed in receive logic of the stylus to achieve synchronization. Current flowing into the stylus tip may be affected by various capacitances and other conditions.